The electrical machine can fundamentally be designed in any way and utilized in any field. Especially preferred, the electrical machine finds use in the motor vehicle sector, in particular as a traction machine for a motor vehicle. The electrical machine is preferably designed as a synchronous machine, in particular as a three-phase synchronous machine. Preferably, the electrical machine is permanently excited. However, it is also possible to provide an electrical excitement. For example, the electrical machine is present as a brushless direct current motor, that is, a so-called BLDC motor.
The electrical machine is multiphase in construction, wherein the inverter associated with the electrical machine is provided for actuating the individual phases of the electrical machine. The inverter has a plurality of strands, namely, preferably just as many as the phases of the electrical machine. Arranged in each of the strands is at least one switch; preferably, a plurality of switches is provided in each case. For example, in each of the strands, both a high-side switch and a low-side switch are formed, wherein each phase of the electrical machine is connected, respectively, between the high-side switch and the low-side switch to the corresponding strand of the inverter.
In this regard, each phase of the electrical machine is connected or can be connected by way of the high-side switch of the corresponding strand to a first electric potential and by way of the low-side switch to a second electric potential. This means that, when the high-side switch is closed, the corresponding phase of the electrical machine is connected to the first electric potential and, when the high-side switch is open, the corresponding phase is decoupled from it. Analogously to this, when the low-side-switch is closed, the corresponding phase of the electrical machine is connected to the second electric potential and, when the low-side switch is open, the phase is decoupled from it. For example, the electrical machine has three phases and, accordingly, the inverter has three strands, so that, in a preferred embodiment, the inverter has three high-side switches as well as three low-side switches.
It is provided that the inverter is actuated by means of pulse width modulation. In this case, a pulse duty factor is determined and adjusted at the inverter. For example, each of the switches, that is, preferably each of the high-side switches as well as each of the low-side switches, is actuated using a respective pulse duty factor. For example, for each of the strands or for each of the phases, a separate pulse duty factor is determined. However, it can also be provided that only a single pulse duty factor is determined and subsequently used for actuating the strands or phases, respectively. It is noted that, also in the determination of a plurality of pulse duty factors, said factors can obviously take on the same value, at least temporarily.
It can be provided, for example, that the electrical machine is actuated or controlled by means of a field-oriented control or a vector control, respectively. The field-oriented control has a rotating vector system and, as input values, the non-rotating currents Id and Iq. The physical actuation of the electrical machine occurs from an intermediate circuit voltage by means of pulse width modulation. The pulse duty factor of the pulse width modulation is formed by means of classical control loops from an actual current intensity and a desired current intensity. Because, via the electrical machine, the current intensity of the electric current is proportional to its torque, it is possible by means of the pulse width modulation to adjust a constant torque for a constant desired current intensity.
When, however, for example, the electrical machine is adjusted or is to be adjusted to a desired rotational speed, this then requires a master control loop, from which a cascade control results. In other words, first of all, an actual rotational speed of the electrical machine is regulated to a desired rotational speed, from which a desired torque or a desired current intensity results. Subsequently, the actual current intensity of the electric current flowing through the electrical machine is adjusted to the desired current intensity.